This invention relates to a dual function exposure time display and control circuit for a TTL (Through the Taking Lens) single lens reflex camera.
In a single lens reflex camera with an automatic exposure time control device, after the reflecting mirror is raised the disphragm is stopped down to a preset value, and light passing through the lens is reflected by the front shutter curtain or the film surface onto a light sensing element mounted in the camera or mirror box. The sensing element output is thus proportional to the brightness of the photographic object, and together with other factors such as film sensitivity, is used to determine and control the exposure time. Initially, the lowered mirror, which includes a beam splitter, passes through light which is reflected onto the sensing element, and the output thereof, together with other factors, is employed for calculating and displaying the exposure time.
Since the lens is stopped-down in the exposure time control mode, any stop value error in the photographic lens can be theoretically disregarded and the exposure accuracy is accordingly high.
If the exposure time is preselected the diaphragm is stopped-down and the photographic operation is controlled in the stopped-down metering mode. In such a case, however, the viewfinder is relatively dark, and it is therefore difficult to establish the picture frame and accurately focus the camera on the object. In addition, the quick operation of the camera is greatly impeded. These factors constitute significant disadvantages of a conventional single lens reflex camera.